The bore polishing wear of supercharged Diesel engine cylinders, which occurs in the form of glossy polished arecs, con lead ta excessive cil consumption, ring and bore scuffing then seizure. As the result,the phenomenon limits the turbocharging development of such engines. Fine surface-analysis techniques are used ta show that such wear is generated by the abrasive effect of upper piston deposits having a structure depending mainly on lubricant composition and, to a certain extent, on that of the fuel.